The present invention relates generally to genetic procedures involving oilseed Brassica napus plants and relates more particularly to procedures intended to increase yield potential of oilseed hybrids having a growth habit of a spring line, by introgression of winter germplasm.
Brassica napus is the most productive oilseed rape. Edible oilseed rape ("canola") is a desirable edible oil produced by certain B. napus which contains less than 2% erucic acid in the oil and less than 30 micromoles of oil-extracted aliphatic glucosinolates per gram of air-dried meal. Canola oil has the lowest percentage concentration of saturated fatty acids of commonly used vegetable oils. Other B. napus produces inedible oils having utility as an industrial lubricant.
Phylogenetic restriction fragment length polymorphism ("RFLP") analyses have differentiated the germplasm of oilseed B. napus into two main groups: winter lines (used in most of Europe) and spring lines (used mostly in northern Europe and Canada). A third, intermediate, category includes East Asian and Australian genotypes that have both growth habits. Diers, B. W. and T. C. Osborn, "Genetic Diversity of Oilseed Brassica napus Germplasm Based on Restriction Fragment Length Polymorphisms," Theor. Appl. Genet. 88:662-668 (1994), incorporated herein by reference.
Winter lines are generally recognized as producing higher seed yields than spring lines. However, in northern latitudes, typified by the northern tier United States and Canada, existing winter lines are not sufficiently hardy to endure overwintering. Thus, only lower-yielding spring lines can grow. Typical spring lines now grown in Canada have an average yield of approximately 1300 kg/ha, whereas yields of 3000 kg/ha are realized in countries that grow essentially all winter rapeseed. Despite these low yields, the spring lines are acceptable in Canada and in the very northern tier United States, insofar as the short growing season and harsh winter do not allow for high yields of any crop. To be economically viable throughout more of the northern tier states, oilseed B. napus lines should yield at least about 2,325 kg/ha or 2000 lb/acre. See Oplinger, E. S. et al., Alternative Field Crops Manual-Canola (Rapeseed) (1989).
Spring/winter growth habit in B. napus appears to be under oligogenic control. Thurling, N. and L. D. Vijendra Das, "Genetic Control of Pre-Anthesis Development of Spring Rape (Brassica napus L.). II. Identification of Individual Genes Controlling Developmental Pattern," Aust. J. of Agric. Res. 30:261-271 (1979); Van Deynze, R. and K. P. Pauls, "The Inheritance of Seed Colour and Vernalization Requirement in Brassica napus Using Doubled Haploid Populations," Euphytica 74:77-83 (1994).
B. napus hybrids are known to exhibit heterosis or hybrid vigor. Sernyk, J. L. and B. R. Stefansson, "Heterosis in Summer Rape (Brassica napus L.)", Can. J. Plant Sci. 63:407-413 (1983); Grant, I. and W. Beversdorf, "Heterosis and Combining Ability Estimates in Spring-Planted Oilseed Rape (Brassica napus L.)," Can. J. of Genet Cytol., 27:472-478 (1985); Lefort-Buson et al., "Heterosis and Genetic Distance in Rapeseed (Brassica napus L.): Crosses Between European and Asiatic Selfed Lines," Genome 29:413-418 (1987); Brandle, J. E. and P. B. E. McVetty, "Heterosis and Combining Ability in Hybrids Derived from Oilseed Rape Cultivars and Inbred Lines," Crop Sci. 29:1191-1195 (1989). Among spring cultivars, higher heterosis levels are observed in offspring of distantly related crosses, such as a cross between the Canadian spring cultivar Regent and the Australian spring cultivar Marnoo (Brandle and McVetty, supra; Diers, et al., "Relationship Between Heterosis and Genetic Distance Based on Restriction Fragment Length Polymorphism Markers in Oilseed Rape (Brassica napus)," Crop Sci. 36:79-83 (1996).
Notably, spring and winter growth habits can be distinguished from one another by RFLPs linked to distinct vernalization-responsive flowering time loci. Ferreira, M. E., et al., "Mapping Loci Controlling Vernalization Requirement and Flowering Time in Brassica napus," Theor. Appl. Genet. 98:727-732 (1995); see also Osborn, T. C. et al, "Comparison of Flowering Time Genes in Brassica rapa, B. napus, and Arabadopsis thaliana," Genetics 146:1123-1129 (1997). A major vernalization-responsive flowering time locus (vfn1; formerly vn1) was mapped as a quantitative trait locus ("QTL") of Linkage Group (LG) 9 using RFLP markers in a doubled haploid population derived from the cross of a European winter cultivar (Major) and a Canadian spring cultivar (Stellar). Vernalization appears to have great influence on the effect of this major gene. In the same doubled haploid population, a second vernalization-responsive flowering time locus (vfn2; formerly vn2) was RFLP-mapped as a QTL of LG12, and a third such gene (vfn3; formerly vn3) was mapped to LG16. The vfn3 gene appears to be less critical to flowering time. The locations of these genes were determined using Mapmaker-QTL.
What is desired is an oilseed B. napus line having a spring growth habit and higher seed yield potentials than other lines that can grow in an environment that supports lines having spring growth habit. Such a hybrid would provide farmers with additional market options and new choices for crop rotation.
The papers noted in this Background are incorporated herein by reference.